Composite catalyst for depolymerization of polyolefins

Abstract

A catalytic composition and method of use for depolymerizing polyolefin-based waste into useful petrochemical products are described. The composition is a complex of at least one zeolite catalyst and one or more co-catalysts that are solid inorganic materials. These composite catalysts, along with heat, are used to increase the depolymerization rate of the feed stream and suppress any potential poisoning effects from non-polyolefin polymers. This results in shorter residence times in the depolymerization unit and a more efficient process.

Description

[0001] Prior related applications

[0002] This application is filed pursuant to the Patent Cooperation Treaty and claims priority to U.S. Provisional Patent Application No. 63 / 122,218, filed December 7, 2020, which is incorporated herein by reference in its entirety.

[0003] Federally Funded Research Statement

[0004] not applicable.

[0005] Reference Microfilm Appendix

[0006] not applicable. Technical Field

[0007] This disclosure relates to catalytic compositions for depolymerizing polyolefin-rich plastic waste to form useful petrochemical products. Background Technology

[0008] Rising living standards and increased urbanization have led to increased demand for polymer products, particularly polyolefin plastics. Polyolefins are frequently used in commercial plastics applications due to their outstanding performance and cost characteristics. For example, polyethylene (PE) has become one of the most widely used and recognized polyolefins because it is strong, extremely tough, and very durable. This allows it to be highly engineered for a wide range of applications. Similarly, polypropylene (PP) is mechanically strong yet flexible, heat-resistant, and resistant to many chemical solvents, such as alkalis and acids. Therefore, polypropylene is ideal for a variety of end-use industries, primarily for packaging and labeling, textiles, plastic parts, and various types of reusable containers.

[0009] A downside to the demand for polyolefin plastics is the increase in waste. Post-consumer plastic waste typically ends up in landfills, with approximately 12% being incinerated and about 9% transferred to recycling. In landfills, most plastics do not degrade rapidly, becoming a major source of waste that overloads landfills. Incineration is also not an ideal solution for treating plastic waste, as it leads to the formation of carbon dioxide and other greenhouse gas emissions. Therefore, there is great interest in developing methods for recycling plastic waste to reduce landfill burdens while also being environmentally friendly.

[0010] One drawback of plastic waste recycling is the difficulty in successfully producing commercially usable or desirable products. Currently, plastic waste recycling involves washing and mechanically reprocessing the material; however, the resulting pellets remain contaminated with food residues, dyes, and fragrances. These contaminants make the pellets undesirable for most applications, based on performance and appearance. Furthermore, obtaining a pure stream of any particular polymer is difficult, meaning that mixed plastic waste streams may not possess the desired properties after recycling.

[0011] Recent advances have focused on converting polyolefin plastic waste into usable products, such as fuel sources or commercially important raw materials. Methods have been developed that involve the pyrolysis of plastic waste streams followed by catalytic depolymerization to produce a variety of products: gases, gasoline fractions, kerosene fractions, diesel fractions, and waxes. Unfortunately, the catalysts themselves are often susceptible to poisoning by other chemicals in the polyolefin waste feedstock, resulting in costly and time-consuming processes, as they require significant energy to completely break down the polyolefin waste into useful product classes.

[0012] Despite progress in polyolefin recycling, there remains a need to develop reliable processes for converting polyolefin-rich waste feedstocks into useful petrochemical products. Ideally, these processes would overcome the "poisoning" effect of other polymers and contaminants that may be present in the waste feedstock. Summary of the Invention

[0013] This disclosure provides novel compositions and methods for the pyrolysis of polyolefin-based materials under anaerobic conditions. The compositions of this disclosure are complexes of multiple catalysts with a synergistic effect to increase the rate of the depolymerization reaction while also suppressing any poisoning effects from non-polyolefin components (NPCs) that may be present in the feed stream or from degradation products of non-polyolefin components. Specifically, a zeolite catalyst is mixed with at least one solid inorganic co-catalyst to form a robust depolymerization composite catalyst. This robust depolymerization composite catalyst is then mixed with polyolefin-based waste in a depolymerization unit and heated under anaerobic conditions in a process called pyrolysis to rapidly generate useful petrochemical products.

[0014] More specifically, zeolites have been found to be useful for the catalytic cracking of polyolefin waste. Zeolites initiate cationic depolymerization of polyolefins, which proceeds at a faster rate (and with a shorter depolymerization half-life) than depolymerization reactions occurring without zeolites, and typically at lower temperatures. However, the catalytic capacity of zeolites can be inhibited by non-polyolefin components that may be present in the feed stream or by degradation products of non-polyolefin components generated during the depolymerization process. In particular, non-polyolefin components, such as nitrogen-containing or high-oxygen-content polymers (including polyamides, polyurethanes, cellulose, and lignin), are known to form degradation products that “poison” the catalytic capacity of zeolites. Alternatively, nitrogen-containing pigments used in consumer products may poison the catalytic capacity of zeolites. These products may not deactivate the catalyst to the extent that they interfere with the depolymerization mechanism, thus slowing the rate. Depending on the type and concentration of zeolites and non-polyolefin components, the rate of depolymerization can be reduced by up to 85% or more, depending on the amount of the unwanted component. Therefore, the amount of energy and time required to depolymerize polyolefins using zeolites increases due to the presence of non-polyolefin components.

[0015] A novel composite catalyst combining at least one zeolite with at least one solid inorganic co-catalyst is disclosed. This composite catalyst addresses the influence of non-polyolefin components on zeolite during pyrolysis, where the co-catalyst restores the catalytic activity of the zeolite. Furthermore, it was found that even when zeolite-inhibiting components or degradation products are absent from the feed stream, the components of the composite catalyst exhibit a synergistic effect on increasing the depolymerization rate of polyolefins. This results in a faster depolymerization reaction compared to depolymerization without the composite catalyst or using only zeolite. The liquid depolymerization products can then be used as is or further processed, for example, in an olefin cracker, as alternative feedstocks.

[0016] The composite catalysts and methods described herein can be used to treat any polyolefin material, including post-industrial waste and post-consumer applications, and may include mixed polyolefin / non-polyolefin streams. The treatment of post-consumer polyolefin waste is particularly important due to landfill overload and the potential for feedstock generation from waste. The methods described herein involve treating post-consumer waste after sorting at a treatment facility in a landfill or other recycling center to separate polyolefin-based materials from other recyclable materials such as glass or metals. However, due to the ability of solid inorganic co-catalysts to suppress any negative impact these non-polyolefin components and / or their degradation products may have on zeolite, complete removal of non-polyolefin polymers, such as cellulose (paper), polyethylene polymers, nylon, etc., is not necessary.

[0017] This disclosure includes any combination of the following embodiments:

[0018] A composite catalyst for depolymerizing polymers, comprising at least one zeolite and at least one solid inorganic co-catalyst.

[0019] A method for depolymerizing a polymer includes adding a polyolefin-based feed stream and a composite catalyst to a reactor heated to a temperature between about 200°C and about 600°C, wherein the composite catalyst comprises at least one zeolite and at least one solid inorganic co-catalyst; and reacting the polyolefin-based feed stream with the composite catalyst to depolymerize the polyolefin-based feed stream.

[0020] A method for depolymerizing a polymer includes: adding a polyolefin-based feed stream and a composite catalyst to a reactor heated to a temperature between about 200°C and about 600°C, wherein the composite catalyst comprises at least one zeolite and at least one solid inorganic co-catalyst, wherein the polyolefin-based feed stream has at most 10 wt.% non-polyolefin component; and reacting the polyolefin-based feed stream with the composite catalyst to depolymerize the polyolefin-based feed stream.

[0021] A method for depolymerizing a polymer includes adding a polyolefin-based feed stream and a composite catalyst to a reactor heated to a temperature between about 200°C and about 600°C, wherein the composite catalyst comprises at least one zeolite and at least one solid inorganic co-catalyst; and reacting the polyolefin-based feed stream with the composite catalyst to depolymerize the polyolefin-based feed stream, wherein the depolymerization rate of the polyolefin-based feed stream is at least 10% higher than the depolymerization rate of a polyolefin-based feed stream without the composite catalyst.

[0022] A method for depolymerizing a polymer includes: adding a polyolefin-based feed stream and a composite catalyst to a reactor heated to a temperature between about 200°C and about 600°C, wherein the composite catalyst comprises at least one zeolite and at least one solid inorganic co-catalyst, wherein the polyolefin-based feed stream has at most 10 wt.% non-polyolefin component; and reacting the polyolefin-based feed stream with the composite catalyst to depolymerize the polyolefin-based feed stream, wherein the depolymerization rate of the polyolefin-based feed stream is at least 10% higher than the depolymerization rate of a polyolefin-based feed stream without the composite catalyst.

[0023] In any composition or method described herein, the solid inorganic co-catalyst is a metal oxide, metal hydroxide, metal carbonate, silicate, or tetravalent metal phosphate.

[0024] In any composition or method described herein, at least one solid inorganic co-catalyst is selected from the group consisting of: Ca(OH)2, Mg(OH)2, Ba(OH)2, Sr(OH)2, CaO, Al2O3 and Zr(HPO4)2.

[0025] In any composition or method described herein, the total amount of the solid inorganic co-catalyst is about 20 to about 90 wt.% of the composite catalyst.

[0026] In any composition or method described herein, wherein the at least one zeolite is selected from the group consisting of: β-zeolite, Socony Mobil-5 zeolite (ZSM-5), ultrastable γ-zeolite, γ-zeolite, or combinations thereof. In some embodiments, H-ultrastable γ-zeolite is used.

[0027] Any composition or method described herein, wherein the composite catalyst includes β-zeolite, ZSM-5 zeolite, Y-zeolite, Ca(OH)2, and Al2O3.

[0028] Any composition or method described herein, wherein the composite catalyst comprises β-zeolite and Ca(OH)2.

[0029] In any composition or method described herein, the composite catalyst is present in an amount greater than 0 to about 20 wt.% of the polyolefin-based feed stream.

[0030] In any composition or method described herein, the polyolefin-based feed stream is low-density polyethylene, high-density polyethylene, polypropylene, or a combination thereof.

[0031] Any composition or method described herein, wherein the polyolefin-based feed stream has at most 10% of at least one non-polyolefin component.

[0032] In any composition or method described herein, at least one non-polyolefin component is a pigment having at least one nitrogen atom.

[0033] In any composition or method described herein, at least one non-polyolefin component is a polymer having a high oxygen content, a nitrogen-containing moiety, or both. In some embodiments, the polymer is selected from the group consisting of nylon polymers, cellulose, polyaramids, polyurethanes, and polyethylene polymers.

[0034] In any composition or method described herein, the polyolefin-based feed stream is post-consumer waste or post-industrial waste.

[0035] Any composition or method described herein, wherein the polyolefin-based feed stream includes both industrial post-waste and post-consumer waste.

[0036] This summary is provided to introduce some concepts that will be further described in the following detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help limit the scope of the claimed subject matter. Attached Figure Description

[0037] Figures 1A to 1BThe half-life of depolymerizing an HDPE feed stream with 3 wt.% cellulose using a composite catalyst having β-zeolite (1A) and ZSM-5 zeolite (1B) mixed with different solid inorganic co-catalysts.

[0038] definition

[0039] As used in this article, “residence time” refers to the time required to depolymerize a batch of polymer waste in the depolymerization unit.

[0040] As used herein, the term "depolymerization half-life" or "half time of depolymerization" refers to the time required for a sample to achieve 50% mass loss at a specific temperature during the TGA pyrolysis reaction. The depolymerization half-life is related to the residence time required in large-scale industrial depolymerization reactors.

[0041] As used in this article, "pyrolysis" refers to a pyrolytic polymerization reaction that occurs in the absence of oxygen.

[0042] The term "pure" used in relation to feed streams refers to feed that is 100% polyolefin, but does not mean that the feed contains only one type of polyolefin. Rather, a "pure" feed stream can contain a mixture of polyolefins such as low-density polyethylene, high-density polyethylene, polypropylene, and combinations thereof.

[0043] Regarding materials, feed streams, or waste streams, the terms "polyolefin-based" and "polyolefin-rich" are used interchangeably to refer to mixtures that are at least 80% polyolefins.

[0044] As used herein, “non-polyolefin component” refers to a material present in a polyolefin-based feed or waste stream that reduces the ability of zeolite to catalyze the depolymerization of polyolefins present in the stream. Examples of non-polyolefin components include non-polyolefin polymers with high oxygen and / or nitrogen content.

[0045] As used in this article, “post-consumer waste” refers to the type of waste generated by the end consumer of the material flow.

[0046] As used in this article, "post-industrial waste" refers to the type of waste generated during the production process of a product.

[0047] As used herein, "feed stream" refers to the supply of polyolefin-based material used for depolymerization. Depending on the depolymerization unit, the feed stream can be a continuously supplied material or a batch of material. The feed stream can be pure polyolefin or a mixture of polyolefin and non-polyolefin components.

[0048] "Waste stream" is a type of feed stream that includes materials that have been discarded and are no longer useful, including but not limited to post-consumer and post-industrial waste.

[0049] As used herein, the terms “poisoning” and “catalyst poisoning” refer to the partial or complete deactivation of a zeolite catalyst by at least one non-polyolefin component in the feed stream to be treated.

[0050] As used herein, the term "zeolite" or "zeolite catalyst" refers to a wide variety of natural and synthetic aluminosilicate crystalline solids whose rigid structure comprises a network of silicon and aluminum atoms tetrahedral coordinated to each other by sharing oxygen atoms. This rigid framework contains channels or interconnected voids that can be occupied by cations such as sodium, potassium, ammonium, hydrogen, magnesium, calcium, and water molecules. The zeolites used herein have a high silica content (Si / Al ratio greater than 5), which not only allows the zeolite's structural framework to withstand the high temperatures used during degradation but also increases the overall acidity of the zeolite. Many zeolites in this disclosure are used in the form of H to ensure the presence of strongly acidic sites.

[0051] Unless otherwise stated, all concentrations in this document are weight percentages (“wt.%”).

[0052] Unless the context otherwise requires, when used in conjunction with the term “comprising” in the claims or description, the use of the words “a” or “an” means one or more.

[0053] The term “about” means the specified value plus or minus the margin of measurement error, or 10% if the measurement method is not specified.

[0054] The use of the term "or" in the claims is intended to mean "and / or" unless it is explicitly stated that it refers only to substitutes or if the substitutes are mutually exclusive.

[0055] The terms “comprising,” “having,” “including,” and “containing” (and variations thereof) are open-ended connecting verbs and allow additional elements to be added when used in claims.

[0056] The phrase “composed of” is closed and excludes all additional elements.

[0057] The phrase “consistent essentially of” does not include additional material elements, but may include non-material elements that do not substantially alter the nature of the invention.

[0058] The following abbreviations are used in this article:

[0059] abbreviation the term beta β (or BEA) zeolite EVA Ethylene vinyl acetate EVOH Ethylene vinyl alcohol H-USY H-Superstable Y Zeolite HDPE High-density polyethylene LDPE Low-density polyethylene MPO Urban polyolefin waste NPC Non-polyolefin components PE polyethylene PET polyethylene terephthalate PP polypropylene TGA Thermogravimetric analysis USY Ultrastable Y zeolite vol.% Volume percentage wt.% weight percentage ZSM-5 SoconyMobil-5 zeolite Detailed Implementation

[0060] This disclosure provides a catalytic composition for recycling polyolefin-based materials into commercially important raw materials. Specifically, at least one zeolite is mixed with at least one solid inorganic co-catalyst to form a composite catalyst for depolymerizing a polyolefin-based feed stream in a depolymerization unit. The components of the composite catalyst work synergistically to increase the depolymerization rate, thereby reducing the amount of time the polyolefin-based feed stream spends in the depolymerization unit. The increase in depolymerization rate even occurs in the presence of non-polyolefin components in the feed stream, which can reduce the catalytic activity of the zeolite in the absence of a solid inorganic co-catalyst.

[0061] Zeolites are solid acid catalysts with an open three-dimensional crystal structure containing numerous pores and acidic active sites where chemical reactions, such as the thermal depolymerization of polyolefins, can occur. Depolymerization proceeds via a hydrogen transfer reaction initiated by the acidic sites of the zeolite and subsequent chain dissociation to generate intermediate carbocations. Essentially, zeolites rely on strongly acidic sites to crack polyolefins. This cracking process begins on the surface of the zeolite because the polymer needs to be broken down into smaller molecules due to the small size of its openings before entering the internal pores of these solids. This results in more contact between the polyolefin and the catalyst, leading to a faster depolymerization rate and a shorter residence time in the depolymerization unit.

[0062] Zeolites offer numerous advantages for depolymerizing polyolefins, including the ability to tune acidity and pore size to address specific feed flow characteristics. Furthermore, zeolites are heterogeneous catalysts, allowing for easy separation and reuse of depolymerization products.

[0063] However, zeolite catalysts are susceptible to poisoning and reduced catalytic activity in the presence of non-polyolefin components (such as polymers with nitrogen-containing groups and / or high oxygen content) and / or their depolymerization products (such as furfural). Furthermore, many substrates with high oxygen and nitrogen content can form coke deposits on zeolite, further reducing its activity. Even after multiple separation steps in recycling facilities, the feed stream of polyolefin waste is rarely pure, and even small amounts of non-polyolefin components can suppress the catalytic ability of zeolite and reduce its depolymerization rate by up to 85%.

[0064] The compositions and methods of the present invention overcome these problems by combining at least one zeolite with a solid inorganic co-catalyst capable of suppressing the poisoning effect of non-polyolefin components from a polyolefin-based feed stream and restoring the ability of zeolite to crack polyolefins. In addition to reducing and / or preventing the inhibition of zeolite by non-polyolefin components, the solid inorganic co-catalyst unexpectedly synergizes with the zeolite, increasing the depolymerization rate of pure or impure polyolefin streams to a greater extent than zeolite alone. The co-catalyst must be and remain solid, as liquid co-catalysts can kill the zeolite catalyst.

[0065] More specifically, the composite catalyst comprises at least one zeolite and at least one solid inorganic co-catalyst. Any zeolite catalyst capable of catalyzing the depolymerization of polyolefins can be used in the composite catalyst. In some embodiments, the composite catalyst comprises commercially available zeolites, including but not limited to β-zeolite (β), Socony Mobil-5 zeolite (ZSM-5), Y zeolite (Y), ultrastable Y zeolite (USY), and amorphous acidic AlSiOx (such as... 40) or combinations thereof. Combinations of zeolites can be used to address specific polyolefin-based feed contents, or to offset the costs associated with using only expensive zeolites in composites.

[0066] The solid inorganic cocatalyst in the composite catalyst of this invention is an inorganic material with acidic or basic characteristics, and can be a silicate, aluminosilicate, carbonate, phosphate, oxide, or hydroxide. As mentioned above, zeolites rely on strongly acidic sites to initiate the depolymerization of polyolefins. Therefore, acidic cocatalyst compounds can be used as cocatalysts without affecting the initiation method of zeolites. However, it has been unexpectedly found that basic cocatalyst compounds can also be used without neutralizing the acidic sites of zeolites or affecting their ability to crack polyolefins. When depolymerizing plastics with acid content (such as polyvinyl chloride), bases such as Ca(OH)2 are used to protect the reactor from corrosion. However, they have not been used for catalytic depolymerization reactions, let alone in combination with zeolites.

[0067] In some embodiments, the solid inorganic cocatalyst is a metal oxide or metal hydroxide. Any known metal oxide or metal hydroxide can be used, including those containing metals from Groups 2 to 8 and 11 to 16, as well as lanthanides and actinides. Exemplary solid inorganic cocatalysts include Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, Sr(OH)₂, NaOH, KOH, CaO, and Al₂O₃. Alternatively, tetravalent metal phosphates (M(HPO₄)₂), where M is Zr, Ti, or Sn, and hydrogen phosphates can also be used. Any combination of solid inorganic cocatalysts can be used. In some embodiments, the composite catalyst has both Al₂O₃ and Ca(OH)₂.

[0068] The amount of solid inorganic cocatalyst in the composite catalyst will depend on the content of the polyolefin feed and the type and amount of the non-polyolefin component (if present) in the feed stream. In some embodiments, the total amount of solid inorganic cocatalyst is about 20 wt.% to about 90 wt.% of the composite catalyst, with the remainder being the total amount of zeolite. In other embodiments, the total amount of solid inorganic cocatalyst is about 20 wt.% to about 60 wt.% of the composite catalyst; alternatively, the total amount of solid inorganic cocatalyst is about 40 wt.% to about 75 wt.% of the composite catalyst; alternatively, the total amount of solid inorganic cocatalyst is about 70 wt.% to about 90 wt.% of the composite catalyst; alternatively, the total amount of solid inorganic cocatalyst is about 50 wt.% to about 75 wt.% of the composite catalyst.

[0069] In some embodiments of this disclosure, the composite catalyst is a combination of β-zeolite with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, Sr(OH)₂, CaO, Al₂O₃, or Zr(HPO₄)₂, wherein the β-zeolite is present in an amount between about 25 and about 50 wt.% of the composite catalyst. Alternatively, the composite catalyst is a combination of ZSM-5 with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, Sr(OH)₂, CaO, Al₂O₃, or Zr(HPO₄)₂, wherein ZSM-5 is present in an amount between about 25 and about 50 wt.% of the composite catalyst. In further embodiments of this disclosure, the composite catalyst comprises a mixture of β-zeolite, ZSM-5, or a combination thereof with Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, Sr(OH)₂, CaO, Al₂O₃, or Zr(HPO₄)₂, wherein the total amount of zeolite present is between about 25 and about 50 wt.% of the composite catalyst.

[0070] The composite catalyst described herein can be used for the thermal degradation or depolymerization of feed streams comprising materials having a single polyolefin component or a mixture of polyolefin components in any amount. Any polyolefin may be present in the feed stream, including but not limited to polyethylene (high-density and low-density), polypropylene, ethylene-propylene copolymers, polybutene-1, polyisobutylene, and copolymers thereof. Furthermore, the feed stream is not limited to any particular form, thus films, foams, textiles, or other molded materials can be treated using the method described. Polyolefins can be obtained from waste streams, including post-consumer waste streams, post-industrial waste streams, or combinations thereof.

[0071] In some embodiments, the feed stream may also include one or more non-polyolefin components that reduce the catalytic activity of the zeolite. Alternatively, the feed stream may also include one or more non-polyolefin components that generate degradation products that reduce the catalytic activity of the zeolite. While many chemicals fall into this category, non-polyolefin polymers are most likely to be present in polyolefin-based feed streams, especially when the feed stream is a waste stream. In particular, non-polyolefin polymers with nitrogen or high oxygen content, such as polyarylamides, acrylates, nylon, polyurethanes, cellulose, and polyethylene polymers, may be present in the feed stream. These polymers are often present in waste sites and are difficult to completely separate from polyolefins. Many of these polymers degrade into problematic products that can reduce the catalytic activity of the zeolite, such as furfural, caprolactam, various amines, phenols, and esters. Alternatively, non-polyolefin components (such as nitrogen-containing pigments) may be present in polyolefin-based waste streams and can reduce the catalytic activity of the zeolite.

[0072] The polyolefin-based feed stream is combined with a composite catalyst and optional additives in a depolymerization unit, where it undergoes a thermal depolymerization reaction catalyzed by the composite catalyst. The depolymerization unit operates at a temperature between about 200°C and about 600°C. Alternatively, the temperature of the depolymerization unit is between about 225°C and about 500°C. In yet another alternative, the temperature of the depolymerization unit is between about 250°C and about 450°C. Due to the residence time required for complete depolymerization of the feed stream, the polyolefin-based feed stream can be processed in batches within the depolymerization unit. Depending on the design of the depolymerization unit, the estimated residence time for each batch is between about 30 and about 300 minutes. Alternatively, the estimated residence time is about 60 minutes.

[0073] The amount of composite catalyst used in the method of the present invention may be limited by the requirements of the depolymerization unit. The composite catalyst is a solid that contributes to the dead volume in the unit during the depolymerization reaction. The lower the dead volume, the more polymer can be depolymerized. In some depolymerization units, the amount of dead volume is limited to 20 vol.% or less. Therefore, in some embodiments of the method of the present invention, the amount of composite catalyst is less than 20 vol.% of the depolymerization unit; alternatively, the amount of composite catalyst is greater than 0 to 10 vol.% of the depolymerization unit; alternatively, the amount of composite catalyst is greater than 8 to 17 vol.% of the depolymerization unit; alternatively, the amount of composite catalyst is greater than 13 to 20 vol.% of the depolymerization unit. In some embodiments, a minimum volume of solids (<3 vol.%) is allowed in the depolymerization unit.

[0074] Depending on the type of depolymerization unit, optional additives (such as sand) can be added to the polyolefin-based feed stream and the composite catalyst mixture. Some of these optional additives may contribute to the dead volume of the depolymerization unit, further limiting the amount of composite catalyst. For example, screw kiln depolymerization reactors use sand as a heat conductor, which limits the amount of dead volume available for the composite catalyst.

[0075] In some embodiments, the composite catalyst is present in an amount of 20% by weight or less of the polyolefin-based batch feed stream. Alternatively, the amount of the composite catalyst is >0 to 5% by weight of the batch polyolefin feed stream. In yet another alternative, the composite catalyst is present in an amount of 2% by weight or 2.5% by weight of the batch polyolefin feed stream. In some embodiments, the amount of the composite catalyst is 10 to 15% by weight of the batch polyolefin feed stream.

[0076] The composite catalysts disclosed herein and the methods for depolymerizing polyolefin-based feed streams using them are illustrated with reference to the following examples. These examples are included to illustrate embodiments of the appended claims. However, these are merely exemplary, and the invention can be broadly applied to any combination of polyolefin-based feed streams and composite catalysts, with and without non-polyolefin components. Those skilled in the art will understand that many changes can be made to the specific embodiments disclosed herein without departing from the spirit and scope of the disclosure, and the same or similar results can still be obtained. The following examples should not be construed as limiting or restricting the scope of the appended claims.

[0077] Example

[0078] Multiple polyolefin-based feedstocks and composite catalysts are combined and depolymerized in a depolymerization unit and analyzed according to the method described above to evaluate the ability of the composite catalyst to catalyze the depolymerization of polyolefin-based compositions.

[0079] Unless otherwise specified, the depolymerization unit is a thermogravimetric analysis (TGA) instrument. For the TGA pyrolysis reaction, a homogeneous sample is heated to the depolymerization temperature of 375 °C at a rate of 10 K / min in a Mettler Toledo TGA / DSC 3+ (Mettler Toledo, Columbus, OH) under nitrogen and held for 1 hour. The depolymerization half-life at a specific temperature is defined as the time required to reach 50% mass loss; if this value is less than 60 minutes, it is recorded directly, or determined as t under the assumption of first-order depolymerization kinetics. 1 / 2 =0.693 / k, where k is the first-order rate constant, which is determined graphically using Ln(C0 / C) on the time plot.

[0080] The depolymerization half-life is related to the residence time required in a large-scale depolymerization unit. The shorter the half-life, the shorter the residence time of a batch of polymer feed in the depolymerization unit, and the faster the depolymerization rate k.

[0081] Example 1: Co-catalyst

[0082] The depolymerization of post-consumer polyolefin waste is complicated by the lack of a polyolefin-only feed stream. Even after multiple separation steps at landfills or recycling centers, some amount of non-polyolefin polymers may remain in the waste feed. These non-polyolefin polymers can interfere with catalysts typically used for depolymerizing polyolefins, such as zeolites. As mentioned above, it is known that nitrogen-containing or high-oxygen-content polymers (such as aromatic polyamides, acrylates, polyurethanes, cellulose, and polyethylene polymers) can “poison” the catalytic activity of zeolites. A series of initial samples were prepared to evaluate whether a solid inorganic co-catalyst could be combined with zeolite to enhance the catalytic activity of zeolite in degrading mixed polyolefin-based feeds.

[0083] A polyolefin-based feedstock was prepared comprising a mixture of high-density polyethylene (HDPE) (grade ACP9255, LyondellBasell product) and 3 wt.% cellulose (Sigma-Aldrich, a high-oxygen-content polymer). Cellulose is a common recyclable material, often present in municipal plastic waste streams as paper or wood impurities. The high oxygen content of cellulose results in numerous degradation products, such as furfural, which can reduce the catalytic activity of zeolites, as shown in Table 1 below. As little as 3 wt.% cellulose resulted in a 14-fold increase in the depolymerization half-life compared to a pure HDPE feedstock.

[0084]

[0085] Therefore, zeolite used for polyolefin depolymerization and Figure 1A (β-zeolite, CP811E-75) and Figure 1B The various solid components shown on the x-axis in (ZSM-5, CBV3014H) are combined to determine whether the solid components can act as co-catalysts to counteract any inhibition of zeolite by cellulose and improve the degradation process.

[0086] A homogeneous sample was prepared by melt-blending 4.7 g of HDPE and 0.15 g of cellulose with 0.2 g of a composite catalyst for 5 minutes at 200 °C and 200 RPM in a HAAK MiniCTW mixer. The composite catalyst consisted of 0.15 g of a solid inorganic co-catalyst combined with 0.05 g of β-zeolite or ZSM-5. The homogeneous sample was then heated to a depolymerization temperature of 375 °C at 10 K / min under nitrogen atmosphere and held for 1 hour.

[0087] The results of these initial reactions are shown in Figures 1A to 1BAs shown in Table 1, the depolymerization half-life of HDPE without cellulose or catalyst was 1733 minutes. The addition of cellulose increased the depolymerization half-life to over 2000 minutes. However, the addition of β-zeolite significantly reduced the depolymerization half-life, to 3 minutes for HDPE alone and approximately 42 minutes for HDPE containing 3 wt.% cellulose. The difference in depolymerization half-life between the two samples is attributed to the degradation of the catalytic activity of β-zeolite by cellulose. Although not shown in Table 1, ZSM-5 zeolite (CBV3014H) (a cheaper alternative to β-zeolite) also reduced the depolymerization half-life of HDPE and HPDE containing 3 wt.% cellulose; however, the reduction was not as large as observed with β-zeolite.

[0088] Several solid inorganic components were added to β-zeolite and ZSM-5 zeolite to evaluate their potential as co-catalysts to further reduce the polymerization half-life of polyolefin-based compositions with 3 wt.% cellulose. Figure 1A As shown, the components that showed the greatest improvement in depolymerization half-life were Ca(OH)₂, Al₂O₃ (acidic), CaO, acidic halloysite (Al₂Si₂O₅(OH)), and the natural non-acidic zeolite NM-CA. In fact, compared to β-zeolite itself, CaO and Ca(OH)₂ reduced the depolymerization half-life by approximately 43% and 71%, respectively. The remaining additives did not reduce the depolymerization half-life to a greater extent than β-zeolite alone (talc, CaCO₃), or only slightly altered the depolymerization half-life (Al(OH)₃).

[0089] Figure 1B A second set of results using ZSM-5 as the zeolite is shown. ZSM-5 zeolite is a cheaper alternative to β-zeolite, but as... Figure 1B As can be seen, composite catalysts with ZSM-5 do not increase the degradation rate of current polyolefin-based feed streams to the same extent. However, all combinations result in faster depolymerization than the uncatalyzed depolymerization reaction. The greatest improvement in depolymerization half-life was observed using a combination of ZSM-5 zeolite and Ca(OH)2.

[0090] also, Figures 1A to 1B The study also demonstrates how some solid inorganic materials are better suited to different zeolites. For example, CaO exhibits a second lowest depolymerization half-life when combined with β-zeolite, but a fifth lowest depolymerization half-life when combined with ZSM-5. Therefore, when using ZSM-5, either Ca(OH)2 or Al(OH)3 can be selected.

[0091] The aim is to increase the depolymerization rate to shorten the residence time and thus reduce the cost of polyolefin recycling. Figures 1A to 1BAll the compositions shown are much faster (higher k values) than the uncatalyzed depolymerization reaction of mixed polymer feeds, which will reduce costs. To further reduce costs, composite catalysts can combine more expensive zeolites (such as β-zeolite) with lower-cost zeolites (such as ZSM-5 zeolite or Y-zeolite) without significantly increasing the residence time of polyolefin-based waste in industrial-scale depolymerization units beyond the ability of β-zeolite alone with non-zeolite co-catalysts.

[0092] While all added components in the composite catalyst improved the depolymerization of this particular polymer feed, some potential co-catalysts were found to reduce the depolymerization half-life to a greater extent than other components. For the purposes of this example, components that reduce the depolymerization half-life by about 5% or more compared to β-zeolite were considered "co-catalysts" for the polymer feed mixtures of the present invention and were optimized in later examples. However, using different polymer feed mixtures containing different "poisons" may lead to Figure 1A Some or all of the replacement components will reduce the depolymerization half-life by 5% or more.

[0093] In addition, it is expected that Figures 1A to 1B Similar components in this example can also increase the depolymerization rate, even if they are not included in this instance. For example, Ca(OH)₂ (also known as lime) was chosen for this example because it is the most readily available metal hydroxide. However, other metal hydroxides (such as KOH, Mg(OH)₂, Ba(OH)₂, and Sr(OH)₂) can also be used as co-catalysts. However, for current polyolefin-based feeds, all these similar compounds may not increase the depolymerization rate to the same extent as Ca(OH)₂. Specifically, they may not have the same activity for the same waste feed, as shown in Table 19 for post-consumer waste streams.

[0094] As another example, KOH would not be a suitable cocatalyst for depolymerizing feedstocks containing cellulose. Cellulose decomposes to produce water, which hydrolyzes KOH, turning it into a slurry in the depolymerization unit and thus killing the zeolite. However, KOH can be used as a cocatalyst for polyolefin-based feedstocks containing non-polyolefin materials other than those that produce water. For example, nylon does not produce water.

[0095] The type of polyolefin is not expected to affect the capabilities of the composite catalyst. Table 2 shows the depolymerization results of LDPE (grade NA214, LyondellBasell) mixed with a composite catalyst including cellulose and ZSM-5 zeolite and Ca(OH)2. As previously stated, the composite catalyst increases the depolymerization half-life to a greater extent than either component of the composite material alone.

[0096]

[0097] Based on Tables 1 to 2 and Figures 1A to 1B The results were further evaluated using composite catalysts including CaO, Ca(OH)2, and / or Al2O3 as solid inorganic co-catalysts and zeolites. The results of these evaluations are shown in Examples 2 and 3 below.

[0098] Example 2: The effect of cellulose concentration

[0099] In this example, compositions were prepared to evaluate the performance of composite catalysts comprising β-zeolite with varying amounts of Ca(OH)2 and / or Al2O3 in depolymerizing polyolefin-based compositions with varying amounts of cellulose.

[0100] As previously described, TGA was used to process various samples, and samples were prepared by melt-blending an HDPE and cellulose composition with a composite catalyst having a 1% β-zeolite loading for 5 minutes in a HAAK MiniCTW mixer at 200°C and 200 RPM. The samples were then heated to a depolymerization temperature of 375°C at 10 K / min under nitrogen and held for 1 hour.

[0101] The compositions and their depolymerization half-lives are shown in Table 3.

[0102]

[0103] The results in Table 3 show that each composite catalyst reduced the depolymerization half-life compared to uncatalyzed depolymerization, although increasing the amount of cellulose did indeed increase the depolymerization half-life and slow the reaction rate. Surprisingly, the composite catalyst with increased Al₂O₃ concentration outperformed the composite catalyst with Ca(OH)₂. The composite catalyst with Ca(OH)₂ not only had a longer depolymerization half-life, but for 3 wt.% cellulose, the difference in half-life was approximately 10% with increasing Ca(OH)₂ concentration. In contrast, the composite catalyst with Al₂O₃ had a lower depolymerization half-life (63 min at 0.15 g, compared to 81 min at 0.15 g Ca(OH)₂) and a significantly reduced half-life at higher concentrations. With increasing Al₂O₃ concentration to 0.5 g, the change in depolymerization half-life for 3 wt.% cellulose was approximately 50%.

[0104] For a polyolefin-based feed with 7 wt.% cellulose, the depolymerization half-life is reduced by approximately 45% for the same range of Al2O3 concentrations, compared to approximately 55% for 6 wt.% cellulose with the same range of Al2O3 concentrations.

[0105] The use of a combination of Ca(OH)2 and Al2O3 in composite catalysts does improve the depolymerization half-life, but to a lesser extent than in composite catalysts containing only β-zeolite and Al2O3.

[0106] Another surprising result was an improvement in the depolymerization half-life of HDPE-only streams. Both solid inorganic co-catalysts exhibited a synergistic effect with β-zeolite, allowing the composite catalyst to reduce the depolymerization half-life of HDPE-only feed from 3 minutes (β-zeolite as the sole catalyst) to 1 to 2 minutes. This was unexpected and is attributed to the fact that the solid inorganic co-catalysts did not “see” the β-zeolite in the polymer melt, allowing all composite catalyst components to function without interfering with each other.

[0107] The selection of composite catalysts containing activated alumina was also evaluated at a temperature of 400 °C. These compositions and their depolymerization half-lives at these high temperatures are shown in Table 4. As previously stated, increasing the amount of activated alumina reduced the depolymerization half-life and accelerated the reaction by 1.7 to 2.7 times compared to the reaction without activated alumina.

[0108]

[0109] Therefore, Ca(OH)₂ and / or Al₂O₃ can be used to improve the depolymerization reaction by increasing the depolymerization rate of polyolefins in the presence of cellulose. Al₂O₃, in particular, has been shown to improve the reaction within a certain temperature range.

[0110] Example 3: H-USY zeolite

[0111] Examples 1 and 2 focus on the use of various β-zeolites and ZSM-5 zeolites as composite catalysts. For this example, composite catalysts were prepared using different amounts of different zeolites H-USY with CaO. The compositions and their depolymerization half-lives are shown in Table 5.

[0112]

[0113]

[0114] In the presence of cellulose, H-USY and CaO alone reduce the depolymerization half-life by 1.6 and 1.2 times, respectively. However, compared to the reaction of uncatalyzed HDPE with cellulose, the combination of H-USY and CaO, acting as a composite catalyst, accelerates the depolymerization reaction by two times.

[0115] Example 4: Nylon

[0116] Composite catalysts perform well when polyolefins are mixed with high-oxygen-content polymers such as cellulose. This example evaluates the performance of a composite catalyst when the nitrogen-containing polymer nylon 12 is added to a polyolefin-based feed. The polyolefin-based feed consists of 0.1 g each of nylon 12 (Sigma-Aldrich) and cellulose (grade NA214, LyondellBasell) in LDPE.

[0117] The composite catalyst in this example comprises varying amounts of ZSM-5 zeolite and a solid inorganic co-catalyst. As previously described, TGA was used as the depolymerization unit for each example; however, the samples were heated to a depolymerization temperature of 400°C at 10 K / min under nitrogen and held for 1 hour. Samples were prepared by melt-blending LDPE, nylon 12, and optionally cellulose with the composite catalyst for 5 minutes at 200°C and 200 RPM in a HAAK MiniCTW mixer. Each composition and its depolymerization half-life are shown in Tables 6 through 9.

[0118]

[0119] Comparative composition 1 is LDPE itself and contains no catalyst or non-polyolefin components. This composition has a depolymerization half-life of 144 minutes at 400°C. The rate constant (k) for this depolymerization is 0.0048. This is the baseline value for comparison with the remaining samples in this example.

[0120] Comparative composition 2 combines LDPE with 1 g of cellulose and 1 g of nylon 12, and has ZSM-5 zeolite as the sole catalyst. Without a solid inorganic co-catalyst, ZSM-5 increases the depolymerization half-life at 400 °C to 151 minutes. Comparative example 3, containing only Zr(HPO4)2 without zeolite, increases the depolymerization half-life to 193 minutes. Comparative example 3 shows that both nylon 12 and cellulose slow down the degradation of LDPE, and that both Zr(HPO4)2 and zeolite are inactive.

[0121] The results shown in Table 6 are for the composite catalyst combining ZSM-5 and Zr(HPO4)2. However, the combination of ZSM-5 and Zr(HPO4)2 increases the rate constant by 5 times, thereby reducing the depolymerization half-life by at least 73%, to about 38 minutes (composition 1).

[0122] A significant decrease in the depolymerization half-life was observed as the concentration of the composite catalyst increased from 0.375 g to 0.75 g. Surprisingly, the largest difference in depolymerization half-life was observed when the amount of Zr(HPO4)2 in the composite catalyst increased. Compared to composition 1, doubling the amount of Zr(HPO4)2 in composition 2 resulted in a 9-minute decrease in the depolymerization half-life. However, compared to composition 1, doubling the amount of ZSM-5 in composition 3 resulted in a 6-minute decrease in the depolymerization half-life. This is surprising because in Comparative Example 3, Zr(HPO4)2 itself increased the depolymerization half-life by approximately 34% and was considered inactive. Conversely, ZSM-5 itself in Comparative Example 3 increased the depolymerization half-life by approximately 5% and was considered active. Therefore, it is not expected that increasing the amount of Zr(HPO4)2 in the composite catalyst is a driving force for the decrease in the depolymerization half-life. However, the results in Table 6 show that Zr(HPO4)2 (which is inactive at 0.5 g) significantly enhances the catalytic effect of the composite catalyst when combined with ZMS-5. Therefore, this indicates a synergistic effect between Zr(HPO4)2 and zeolites (such as ZMS-5) when combined.

[0123] The results shown in Table 7 are for composite catalysts combining ZSM-5 with Al2O3 and / or Ca(OH)2.

[0124]

[0125] Solid inorganic cocatalysts both contribute to reducing the depolymerization half-life; however, the reduction is slightly greater when Ca(OH)2 is used in compositions 9 and 10 than in compositions 6 and 7 containing Al2O3. This trend is the opposite of the trend observed in HDPE / cellulose feed in Example 2. It is believed that the addition of nylon 12, rather than the change from HDPE to LDPE, is the reason for the slightly better effect of Ca(OH)2. However, increasing the amount of ZSM-5 eliminates any difference between the two solid inorganic cocatalysts, as both compositions 8 and 11 have a depolymerization half-life of 37 minutes.

[0126] As shown in Table 7, the greatest improvement in depolymerization half-life was observed when the composite catalyst contained 0.25 g of ZSM-5 and 0.5 g of a solid inorganic co-catalyst (approximately 15 wt.% of compositions 8, 11, and 13). These results indicate that while the combination of zeolite and solid inorganic co-catalyst can improve the depolymerization reaction, the amounts of both components can be varied and tailored to each polyolefin feed. Furthermore, the reduction in depolymerization half-life translates to shorter residence times in large-scale industrial reactors.

[0127] The catalyst complex performed well with polyolefin feeds containing only cellulose, as well as nylon and cellulose. Therefore, a series of compositions containing nylon mixed with LDPE were prepared and depolymerized. These compositions and their depolymerization results are shown in Tables 8 and 9.

[0128]

[0129] Table 8 shows a series of feeds containing 0.5 g of nylon 6. Adding nylon 6 to composition 14 increased the depolymerization half-life from 144 minutes (comparative composition 1) to 161 minutes. Adding zeolite to composition 15 did not improve the depolymerization half-life of the LDPE / nylon 6 feed. Conversely, adding Ca(OH)₂ reduced the depolymerization half-life to 139 minutes, which was less than the depolymerization half-life observed in comparative composition 1. However, the results for composition 17 showed a synergistic effect of the combination of zeolite and Ca(OH)₂. The composite catalyst in composition 17 reduced the depolymerization half-life by approximately 42% to 83 minutes.

[0130] Table 9 shows a series of feeds with different amounts of nylon 12. Unlike the effect of nylon 6 in composition 14, adding 0.5 g of nylon 12 reduced the depolymerization half-life from 144 min (comparative composition 18) to 107 min. Adding zeolite to composition 19 slightly reduced the depolymerization half-life to 103 min. Adding Ca(OH)2 to composition 20 increased the depolymerization half-life to 124 min. However, the combination of zeolite and Ca(OH)2 in composition 21 increased the depolymerization half-life even further to 131 min. These results show that with increasing amounts of non-polyolefin components, such as 0.5 g of nylon, higher composite catalyst loadings are required to compensate for the loss of reaction rate.

[0131]

[0132] Compositions 22 to 28 use a smaller amount of nylon 12. All compositions using Ca(OH)2 as a cocatalyst are able to improve the depolymerization reaction by reducing the half-life.

[0133] Furthermore, increasing the amount of zeolite in the composite catalyst showed further improvement. For example, the depolymerization half-life of composition 25 containing 0.25 g of zeolite was 54 minutes shorter than that of composition 23 containing 0.125 g of zeolite. The same amount of Ca(OH)₂ was used in both compositions.

[0134] Compositions 26 to 28 contain Al₂O₃ instead of Ca(OH)₂ as a solid inorganic cocatalyst. This cocatalyst has a more active effect on the depolymerization reaction than Ca(OH)₂. This is unexpected, as composition 26, without zeolite, has a higher half-life than control composition 1. However, when combined with zeolite, Al₂O₃ has a synergistic effect, resulting in a reduction of the depolymerization half-life by at least 88%.

[0135] Example 5: Other polymer compositions

[0136] Composite catalysts perform well when polyolefins are blended with high-oxygen-content polymers (such as cellulose) and high-nitrogen-content polymers (such as nylon 6 and 12). In this example, a series of feeds containing various polymer combinations were depolymerized using ZSM-5, Ca(OH)2, and composite catalysts including both ZSM-5 and Ca(OH)2. The results are shown in Tables 10 to 15 and can be compared with the 144-minute depolymerization half-life of a sample containing only LDPE.

[0137]

[0138] The feeds listed in Table 10 include polyurethane. The addition of polyurethane alone increased the depolymerization reaction time by 16 minutes. Compared to the uncatalyzed reaction, the composite catalyst reduced the depolymerization half-life by approximately 47%, and by approximately 56% compared to the reaction with Ca(OH)₂ alone.

[0139]

[0140] The feedstocks listed in Table 11 include ethylene vinyl alcohol (EvOH). Compared to the uncatalyzed reaction, the composite catalyst reduces the depolymerization half-life by approximately 94%.

[0141]

[0142]

[0143] The feedstocks listed in Table 12 include ethylene vinyl acetate (EVA). Compared to the uncatalyzed reaction, the composite catalyst reduced the depolymerization half-life by approximately 98%. Surprisingly, this is the same reduction achieved by the composition using only ZSM-5 zeolite.

[0144]

[0145] The feeds listed in Table 13 include aryl copolymers. The addition of aryl copolymers alone increased the depolymerization reaction time by 22 minutes. Compared to the uncatalyzed reaction, the composite catalyst reduced the depolymerization half-life by approximately 89%.

[0146]

[0147] The feeds listed in Table 14 include PET. The addition of PET alone increased the depolymerization reaction time by 5 minutes. Four different non-catalytic reactions were conducted. Compared to the non-catalytic reactions using the same feeds, the composite catalyst reduced the depolymerization half-life by approximately 98.5%.

[0148]

[0149] The feeds listed in Table 15 include polybutyl methacrylate (PBMA). The addition of PBMA alone increased the depolymerization reaction time by 25 minutes. Compared to the uncatalyzed reaction using the same feeds, the composite catalyst reduced the depolymerization half-life by approximately 72%.

[0150] In all samples in Example 5, the use of a composite catalyst comprising ZSM-5 zeolite and Ca(OH)2 reduced the depolymerization half-life by more than about 50%. Except for feedstocks containing polybutyl methacrylate and plastic water bottles, the composite catalyst exhibited properties similar to or superior to those of the zeolite itself.

[0151] Example 6: Post-consumer waste

[0152] This example focuses on the synergistic effect of combining zeolite with solid inorganic co-catalysts on the depolymerization of polyolefin-based post-consumption waste streams.

[0153] Granulated Polyolefins: The first post-consumer waste stream evaluated was obtained from a classified post-consumer waste stream consisting primarily of polyolefins (>90% HDPE content, SUEZ Corp.) and then granulated. As previously mentioned, the depolymerization unit was a TGA instrument. Homogeneous samples were prepared by melt-blending 5 g of the granulated post-consumer waste stream with various catalysts for 5 minutes at 200 °C and 200 RPM in a HAAK MiniCTW mixer. The homogeneous samples were heated to a depolymerization temperature of 400 °C at a rate of 10 K / min under nitrogen in a Mettler Toledo TGA / DSC 3+ (Mettler Toledo, Columbus, Ohio) and held for 1 hour.

[0154] Four different catalysts were used to depolymerize the granular post-consumer waste stream. The first catalyst consisted of only 0.25 g of β-zeolite, used in composition 15. The second catalyst consisted of only 0.25 g of amorphous AlSiOx zeolite, used in composition 16. The third catalyst consisted of only ZSM-5 zeolite, used in different amounts in compositions 17 to 18. The final catalyst was a composite catalyst consisting of 0.375 g of a co-catalyst combined with 0.25 g of ZSM-5 zeolite. The composite catalyst was used in compositions 19 to 21. The compositions and depolymerization half-lives are shown in Table 17.

[0155]

[0156] The depolymerization half-life of Comparative Example 17, without catalytic depolymerization, was 239 minutes. The depolymerization half-life decreased with the addition of a catalyst (zeolite or composite catalyst). For mixtures containing only zeolite, 0.25 g of zeolite (5% of the mixture) produced the fastest depolymerization half-life. In Comparative compositions 17 to 18, reducing the amount of ZSM-5 increased the depolymerization half-life by more than three times.

[0157] The composite catalyst used the same amount of zeolite as the mixture in composition 18. Compared to composition 18 using only 0.125 g of ZSM-5 zeolite, the observed depolymerization half-life was reduced by more than half when composite catalysts of compositions 19 to 20 were used regardless of the co-catalyst. This demonstrates the synergistic effect of the co-catalyst when combined with zeolite. It is also noted that the use of Zr(HPO4)2 with ZSM-5 showed an improvement over composition 18, which used a larger amount of ZSM-5, again demonstrating the synergistic effect of the co-catalyst and zeolite.

[0158] Shredded Municipal Polyolefins: The second post-consumer plastic stream evaluated was a shredded municipal polyolefin waste stream (MPO) consisting of a combination of PE and PP (approximately 1:1). As previously mentioned, the depolymerization unit was a TGA instrument. Homogeneous samples were prepared by melt-blending 5 g of the MPO stream with 0.125 to 0.25 g of zeolite or 0.375 to 0.5 g of composite catalyst in a HAAK MiniCTW mixer at 200 °C and 200 RPM for 5 minutes. The composite catalyst consisted of 0.25 g of co-catalyst combined with 0.125 g or 0.25 g of zeolite.

[0159] The homogeneous sample was heated to a depolymerization temperature of 400 °C at a rate of 10 K / min in a Mettler Toledo TGA / DSC 3+ atmosphere in Columbus, Ohio, and held for 1 hour. The depolymerization half-life is shown in Table 18.

[0160]

[0161] Comparative composition 18 is a catalyst-free MPO and provides a baseline depolymerization half-life of 204 minutes. Similar to granular polyolefins, the depolymerization half-life of MPO decreases with the addition of a catalyst. The observed depolymerization half-life is also reduced by at least 10% when using a composite catalyst (regardless of the type of co-catalyst) compared to using zeolite alone. In fact, the addition of a solid inorganic co-catalyst to the β-zeolite in compositions 26 and 27 reduces the half-life by 75% compared to composition 25. Therefore, this demonstrates that the composite catalyst of this disclosure is significantly more effective than either component used alone.

[0162] Multilayer Packaging Films: Table 19 shows the depolymerization results of post-consumer multilayer packaging film waste, where a composite catalyst combines various zeolites with one of Al₂O₃, Ca(OH)₂, Ba(OH)₂, Mg(OH)₂, or Sr(OH)₂. The multilayer film mixtures include polyolefin packaging films with adhesive bonding layers and barrier films bonded therein. These adhesive bonding layers and barrier films are formed from non-polyolefin polymers (such as EVA, EVOH) and polyamines.

[0163] Adding Ca(OH)₂ to each of the zeolites in Table 19 resulted in a decrease in the depolymerization half-life. In fact, Ca(OH)₂ itself was able to reduce the half-life from 330 minutes (comparative composition 19) to 248 minutes (composition 31). However, unexpectedly, increasing the amount of Ca(OH)₂ did not result in a large change in the depolymerization half-life. Composition 39 contained twice the amount of Ca(OH)₂ as composition 38, but only reduced the half-life by another two minutes (~5%). See also compositions 42 and 43, where doubling the weight of Ca(OH)₂ effectively increased the half-life by approximately 70%. However, this difference in half-life can also be attributed to the component ratios, where composition 42 was a 1:1 ratio and composition 43 was a 1:4 ratio (zeolite: Ca(OH)₂). In any case, for this particular feed stream, 5 wt.% Ca(OH)₂ in addition to the zeolite is required to see a positive effect.

[0164] Compared to catalysts containing only zeolite, the addition of Mg(OH)₂ also reduced the depolymerization half-life. In contrast, the addition of Ba(OH)₂ and Sr(OH)₂ increased the depolymerization half-life, thereby slowing down the depolymerization rate of this particular waste feed. However, for other types of feed, or using feeds with different particle sizes, their activity may exceed that of Ca(OH)₂ and Mg(OH)₂.

[0165] Table 19 also shows the use of Al2O3 with two different ZSM-5 zeolites in compositions 33 and 41. However, only composition 33 showed an improved depolymerization half-life compared to compositions containing only zeolites, further suggesting that different combinations of the same components may not be as effective for the same feed stream.

[0166]

[0167] These reductions in the depolymerization half-life experienced by each post-consumer waste stream in Example 6 translate into shorter residence times in large-scale industrial reactors. Furthermore, the results demonstrate the synergistic effect of solid inorganic co-catalysts when combined with zeolites, even in the absence of non-polyolefin components in the feed stream. These results also indicate that the composite catalysts of this disclosure are suitable for depolymerizing real-world feed streams obtained from post-consumer sources.

[0168] The examples above have demonstrated that the catalytic composition of zeolite and at least one solid inorganic cocatalyst described in this invention can catalyze the depolymerization of polyolefin-based streams with improved energy efficiency (i.e., greater cost-effectiveness) compared to methods without the use of a cocatalyst. Improvements in the depolymerization reaction have been observed even when the polyolefin-based stream contains other polymers that can suppress the catalytic ability of the zeolite, or when the feed stream is obtained from a post-consumption source.

[0169] Example 7: Zeolite / Supported Zr(HPO4)2 Catalyst System

[0170] A homogeneous polyolefin-based sample was prepared by melt-blending 2.5 g of high-density polyethylene (HDPE; grade ACP9255, LyondellBasell), 2.5 g of polypropylene (MOPLEN HP522H, LyondellBasell), 0.25 g of nylon 6 (Sigma-Aldrich), 0.125 g of H-USY catalyst, and specified amounts of additives for 5 minutes in a HAAK MiniCTW mixer at 200 °C and 200 RPM.

[0171] The homogeneous sample was heated to a depolymerization temperature of 400 °C at a rate of 10 K / min in a Mettler Toledo TGA / DSC 3+ (Mettler Toledo, Columbus, Ohio) and held for 1 hour.

[0172] The compositions and their depolymerization half-lives are shown in Tables 20 and 21. As shown therein, the Zr(HPO4)2-based additives prepared by reacting ZrOCl2 with phosphoric acid or ammonium phosphate in the presence of a support are effective in the depolymerized samples.

[0173] Additive manufacturing SiO2-supported ZrP additives are formed via a pre-wetting technique. For example, silica is impregnated with a solution of ZrOCl2 (Sigma-Aldrich) in H2O and the resulting mixture is then heated at 110°C. ℃ Dry for 2 hours. The resulting powder was impregnated with varying amounts of H₂PO₄ solution (Sigma-Aldrich) to produce [a product] at 110 [units unclear]. ℃ Free-flowing powder dried for 2 hours. Bentonite (F-20X, Engineered Clays Co.) supported ZrP additive is similarly formed by reacting ZrOCl2 with a phosphorus-containing reagent. For example, a bentonite sample is kneaded / mixed with 30 ml of ZrOCl2 in H2O solution, and the resulting paste is dried at 110 °C. ℃Dry for 2 hours. Then knead / mix the resulting powder with various amounts of H2PO4 solution or ammonium phosphate (mono- or dibasic; Sigma-Aldrich) to produce a product at 110 ℃ The paste was dried for 2 hours.

[0174]

[0175]

[0176]

[0177] The above examples demonstrate that, compared with methods that do not use additives, the catalyst composition of zeolite and at least one zirconium-based additive described in this invention can catalyze the depolymerization of polyolefin-based streams more rapidly.

[0178] Example 8: ZEOLYTE / ZrHP catalyst system 1

[0179] The following experimental steps were performed in a depolymerization apparatus comprising a jacketed reactor with mechanical stirring. This jacketed reactor has an inlet for feeding plastic waste from the extruder, an inlet for feeding the depolymerization catalyst, and an outlet for the generated gas. The gas discharged from the reactor is conveyed to a condensation unit, from which non-condensable gas and pyrolysis oil are obtained. Thermocouples are placed in the reactor to monitor and record the temperature.

[0180] Example 8 uses a plastic waste feedstock comprising 97 wt% polyolefin content and the remainder including trace amounts of other common polymers (e.g., PET, PS, PA, and PU) plus inorganic contaminants. The plastic waste feedstock is homogenized and granulated, then fed into an extruder via a hopper. The extruder operates at 290°C and continuously discharges waste into a depolymerization reactor at a rate of 4 kg / h.

[0181] The depolymerization reactor was operated at a pressure of 4 barg and a temperature of approximately 400°C. The catalyst was continuously injected into the reactor as a suspension in white oil using a syringe system similar to that disclosed in WO2008 / 022900, which is incorporated herein by reference. The total depolymerization time was approximately 3 hours. At the end of the depolymerization phase, the reactor was allowed to cool and be opened for cleaning.

[0182] The gaseous phase generated in the reactor is sent to a condensation unit formed by a cooling / washing tower operating at 25°C. The selected cooling temperature allows heavy hydrocarbons to be condensed and very light hydrocarbons to be released as a gas stream. The gas stream is then delivered to an exhaust port. The condensed oil is analyzed by GC-FID.

[0183] Because of the large number of compounds, the analytical results have been reported by grouping the obtained compounds according to their retention times using specific hydrocarbons as internal retention time references.

[0184] Comparative Example 21: Evaluation of H-USY Zeolite without Additives

[0185] In the process setup described in Example 8, samples of H-USY zeolite type (CBV400 – CAS No. 1318-02-1, Zeolyst International) were tested. The catalyst was fed into the reactor in an amount providing 3 wt.% of the mass of the reaction phase.

[0186] The reactor was operated at 4 barg and the internal temperature was recorded as 403°C.

[0187] The results regarding product yield (relative to feedstock) are reported in Table 22, along with a report on GC-FID analysis of the produced oil samples. The residual content of components excluding those from the inert feedstock (i.e., actual plastic waste) was calculated.

[0188] Example 58 of the present invention: Evaluation of the catalyst system (H-USY + zirconium hydrogen phosphate (IV))

[0189] The experimental test was conducted as described in Comparative Example 21, except that a slurry of white oil was prepared and fed into reactor (1). This slurry contained a mixture of 1:1 wt.% H-USY zeolite type (CBV 400, CAS No. 1318-02-1, available from Molecular Sieve International) and zirconium hydrogen phosphate (IV) (CAS No. 13772-29-7, available from Merck). As used herein, “ZrHP” refers to zirconium hydrogen phosphate (IV).

[0190] The solid catalyst mixture comprises 4 wt% of a combined solid catalyst mixture (2 wt% HY-zeolite + 2 wt% ZrHP) and a reaction phase material. The temperature is maintained at 407°C and the pressure is adjusted to 4 barg. Experimental test results are listed in Table 22 as Example 58 of the present invention.

[0191] Calculate the residual content excluding components from inert feed (i.e., actual plastic waste).

[0192]

[0193] Compared to Comparative Example 21, Example 58 of the present invention exhibits lower residues, indicating higher catalytic activity. The recovered oil of Example 58 of the present invention contains no hydrocarbons with a boiling point above 434°C. Comparative Example 21 contains 3 wt% hydrocarbons with a boiling point above 434°C. Furthermore, compared to 4 wt% in Comparative Example 21, the fraction of the recovered oil in Example 58 with a boiling point between 365°C and 434°C is 2 wt%.

[0194] Example 9: ZEOLYTE / ZrHP catalyst system 2

[0195] 30 grams (30 g) of the same plastic waste raw material prepared as described in Example 8 was loaded into a 500 ml circular glass reactor with three necks equipped with thermocouples and nitrogen inlets. A specific amount of solid catalyst was then introduced into the glass reactor. Two glass condensers were connected in series and maintained at 110°C and -8°C respectively using oil baths (Cryostat Julabo). The reactor was placed in an electrically heated system (i.e., a jacketed bath) and the temperature was raised to 450°C. The pyrolysis process was carried out for 2 hours (maximum), and the oil was recovered and subsequently analyzed.

[0196] Comparative Example 22: Evaluation of H-USY Zeolite without Additives

[0197] Using the experimental setup described in Example 9, samples of H-USY zeolite type (CBV400, CAS No. 1318-02-1, available from Molecular Sieve International) were tested. The catalyst was fed into the reactor to a concentration of 2.5 wt% of the total mass of the catalyst and feedstock.

[0198] The results regarding product yield (relative to feedstock) and the GC-FID analysis of the produced oil samples are reported in Table 23. The residual content of components excluding those from the inert feed (i.e., actual plastic waste) was calculated. The initial temperature (Tinitial) represents the temperature at which the first drop of oil is collected in the first condenser.

[0199] Example 59 of the present invention: Combination system (H-USY + Zirconium hydrogen phosphate (IV))

[0200] Experimental tests were conducted as described in Comparative Example 22, except that ZrHP was incorporated into the catalyst material. The solid catalyst mixture of Example 59 of the present invention comprises 5 wt% of a combined solid catalyst mixture (2.5 wt% H-USY + 2.5 wt% ZrHP) and a reaction phase material. The experimental test results of Example 59 of the present invention are listed in Table 23.

[0201] The residual content of components excluding those from inert feed (i.e., actual plastic waste) was calculated. The residual content of Example 59 of the present invention is comparable to that of Comparative Example 22; however, Example 59 of the present invention produces a higher amount of lighter compounds compared to Comparative Example 22, indicating the production of more pyrolysis products due to increased catalytic activity. For example, the oil fractions of Example 59 below 98°C and between 98°C and 203°C are 25 wt% and 57 wt%, respectively, significantly higher than the equivalent 17 wt% and 45 wt% of Comparative Example 22.

[0202] Comparative Example 23: ZrHP

[0203] Experimental tests were conducted using 30 grams of the same plastic waste feedstock prepared as described in Example 8, in the experimental setup of Example 9. However, in this experiment, only zirconium hydrogen phosphate (IV) (CAS No. 13772-29-7, available from Merck) was added to the plastic waste feedstock. ZrHP comprised 2.5 wt% of the total mass of ZrHP and the reaction phase. The results of Comparative Example 23 are shown in Table 23.

[0204]

[0205] Comparative Example 23 did not show activity as a depolymerization catalyst, leaving a very high residual content (22 wt%) in the reactor and producing an oil comprising a high percentage (70 wt%) of components with boiling points in the range of 203 °C to 434 °C.

Claims

1. A composite catalyst for depolymerizing a polymer, comprising: a) at least one zeolite; and, b) 20 to 90 wt. % of at least one solid inorganic cocatalyst based on the total weight of the composite catalyst, wherein the at least one solid inorganic cocatalyst comprises Zr(HPO4)2.

2. The composite catalyst of claim 1, wherein the at least one zeolite is selected from the group consisting of a beta zeolite, a Socony Mobil-5 zeolite (ZSM-5), a Y zeolite, or a Ultrastable Y zeolite, or a combination thereof.

3. The composite catalyst of claim 1, wherein the at least one zeolite is a beta zeolite.

4. The composite catalyst of claim 3, wherein the beta zeolite is present in an amount of 25 to 50 wt. % based on the total weight of the composite catalyst.

5. The composite catalyst of claim 1, wherein the composite catalyst comprises ZSM-5.

6. The composite catalyst of claim 1, wherein the composite catalyst comprises a beta zeolite and ZSM-5, and wherein the total amount of the beta zeolite and ZSM-5 is 25 to 50 wt. % based on the total weight of the composite catalyst.

7. The composite catalyst of claim 1, wherein the total amount of the solid inorganic cocatalyst is 20 to 60 wt. % of the composite catalyst.

8. A method of depolymerizing a polymer, comprising: a) adding a polyolefin-based feed stream and the composite catalyst of claim 1 to a reactor heated to a temperature between 200 °C and 600 °C; and b) reacting the polyolefin-based feed stream with the composite catalyst to depolymerize the polyolefin-based feed stream.

9. The method of claim 8, wherein the composite catalyst is present in an amount of greater than 0 to 20 wt. % of the polyolefin-based feed stream.

10. The method of claim 8, wherein the polyolefin-based feed stream is a low density polyethylene, a high density polyethylene, a polypropylene, or a combination thereof.

11. The method of claim 8, wherein the polyolefin-based feed stream has at most 10% of at least one non-polyolefin component.

12. The method of claim 11, wherein the at least one non-polyolefin component is a polymer having a high oxygen content, a nitrogen-containing moiety, or both.

13. The method of claim 12, wherein the polymer is selected from the group consisting of a nylon polymer, a cellulose, a polyaramid, a polyurethane, and a polyethylene polymer.

14. The method of claim 13, wherein the polyolefin-based feed stream is a post-consumer waste or a post-industrial waste.

15. The method of claim 11, wherein the at least one non-polyolefin component is a pigment having at least one nitrogen atom.

16. The method of claim 8, wherein the polyolefin-based feed stream comprises both a post-industrial waste and a post-consumer waste.

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